Mixed-Anion Cu(II) Complexes with 3-(pyridin-2-yl)pyrazole (L), Syntheses and X-ray Crystal Structure of [Cu(L)2 Br]ClO4 (L=3-(pyridin-2-yl)pyrazole)

Reaction of the ligand 3-(pyridin-2-yl)pyrazole (L) with Cu(ClO₄)₂ and CuX₂ (X=Cl, Br, I) gives complexes with stoichiometry [Cu(L)₂X]ClO₄ (X = Cl, Br, I). The new complexes were characterized by elemental analyses and infrared and electronic spectroscopy. The crystal structure of the [Cu(L)₂Br]ClO₄ was determined by X-ray crystallography. The cation complex (i.e. [Cu(L)₂Br]P) contains copper(II) with a distorted trigonal bipyramid geometry with a Br^― ligand occupying an equatorial site. The penta-coordinated metal atom is bonded to two pyridinic nitrogens, two pyrazolic nitrogens, and one bromide anion. The pyrazolic H atoms are hydrogen bonded to Br atoms, resulting in infinite hydrogen-bonded chains running in the b direction. There are π‐π stacking interactions (charge-transfer arrays) between the parallel aromatic rings belonging to adjacent chains that may help to form hydrogen bonding in the coordination geometry around Cu (II).